Pre-engineered failure link for brush shaft

ABSTRACT

A sacrificial link is disclosed for the shaft of a vehicle-cleaning brush unit, which link is pre-engineered to fail prior to the remainder of the shaft in response to bending forces exerted on the brush by a vehicle, for example. The shaft itself is therefore protected from permanent deformation or breakage, while the sacrificial link is easily removed and replaced with relatively little downtime and expense. In a preferred form the sacrificial link comprises a sacrificial shaft section having socket ends for removable connection to the upper portion of a brush shaft depending from a motor drive unit and the lower portion of the brush shaft connected to the brush, and a center region pre-engineered to fail before the upper and lower brush shaft sections. Novel clamping and release structure associated with the socket ends of the sacrificial shaft section is also disclosed.

FIELD OF THE INVENTION

The present invention relates to rotary brush units used in vehiclewashes and the like. More specifically, the present invention relates toa brush shaft designed such that, under external force, permanentdeformation is limited to a predetermined portion which can be easilyremoved and replaced without having to disassemble the entire brushunit.

BACKGROUND OF THE INVENTION

A common problem in rotary brush units used in vehicle washes is thepermanent deformation or breakage of the brush shaft. Frequently,vehicles which stray from the proper path or track or which are toolarge or driven too fast run into the brushes with excessive force,causing the brush shaft to bend or break.

A typical prior art overhead brush unit 10 shown in FIG. 1 comprises amotor drive unit, drive/support shaft, and brush. The rotating driveshaft 20 is suspended at its upper end 20a from an overhead, motorizeddrive unit 15. A brush 18 is attached to the shaft at its lower end 20bto rotate with the shaft. Though made of steel or a similar strongmaterial, the drive shaft 20 can be bent when, for example, anautomobile 1 runs into the brush 18. If the force of the collision isgreat enough, shaft 20 can be permanently bent or even broken at abending moment region 27 between the brush and the drive unit. This typeof damage requires disassembly of the entire brush unit 10 in order toreplace the damaged shaft; removing the shaft from the drive unit is aparticularly labor intensive operation. Such damage is also expensivefrom the standpoint of both replacement shaft cost and downtime duringwhich the brush unit, and often the entire wash, is inoperative.

SUMMARY OF THE INVENTION

In the present invention the expense of replacing a bent or broken shaftis eliminated through the use of a sacrificial link, detachablyinterposed between first and second portions of the rotating brushshaft. This link is designed to permanently deform or break prior to theremainder of the shaft. To accomplish this, the sacrificial link ispreferably incorporated between the first and second shaft portions at apoint where the shaft is expected to experience significant bendingmoment in response to external force. The preferred form of thisinvention is further characterized by a sacrificial link having a centerregion whose diameter is smaller than the diameter of either the firstor second shaft portions, making it significantly weaker and the firstto bend. Once permanently deformed, the sacrificial link is easilyreplaced with a minimum of downtime and expense.

In a vehicle-cleaning brush unit having a brush-supporting shaftdepending from a support unit, the brush shaft comprises separate firstand second shaft portions connected to the brush and motor drive unit,respectively, and the sacrificial link is removably connected to thefirst and second shaft portions.

The sacrificial link in one form comprises a sacrificial shaft sectionhaving two ends connected to the first and second shaft portions of thebrush unit, and a center region pre-engineered to fail before the firstand second shafts by virtue of a reduced diameter. The ends of thesacrificial shaft section and the reduced diameter center region arepreferably connected by regions of tapered diameter. The ends caninclude sockets whose diameter is approximately equal to the diameter ofthe first and second shaft portions.

In a further form of the invention the socket ends of the sacrificialshaft section are divided into clamping halves for improved,shear-resistant coupling to the rotating shaft portions. The socket endspreferably further include a tap hole to assist in removing a shaftsection clamped therein should the parts become stuck or corroded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a prior art brush assembly and shaft being bent by anautomobile;

FIG. 2 illustrates a sacrificial brush shaft link according to thepresent invention, as it is incorporated into a brush shaft, also beingbent;

FIG. 3 is an exploded perspective view of the sacrificial link and brushshaft of FIG. 2; and

FIG. 4 is a more detailed perspective view of the sacrificial link ofFIG. 2, showing its connections with a brush shaft in phantom.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

FIG. 1 shows a typical prior art brush unit 10. As depicted, it includesa shaft 20 suspended at its upper region 20a by an overhead drive unit15. A brush 18 is suspended from the opposite end 20b of shaft 20.Excessive force imposed on brush 18 by, for example, an automobile 1 cancause permanent deformation or breakage of the shaft 20. Because theshaft and brush are freely suspended from the drive unit 15, the bendingmoment is concentrated at a point 27 near the drive unit. Since theshaft is connected to both the drive unit 15 and brush 18, repair of thebent or broken shaft requires disassembly of the entire brush unit 10.

In the present invention, shown in FIG. 2, the rotating shaft 30 of theoverhead brush unit 10 comprises three distinct portions: an upper shaftportion 31, connected to and protruding from the drive unit 15; a secondshaft portion 32, connected to and protruding from the brush 18; and asacrificial link 40 removably connected to the free ends of upper andlower shaft portions 31,32 to form a unitary drive/support shaft.Sacrificial link 40 is located where the greatest bending moment isanticipated, in the illustrated embodiment near drive unit 15 at apre-engineered failure area 42.

This three-piece shaft structure alleviates problems of both downtimeand replacement cost when repairing damaged brush shafts. Sinceexcessive force on the brush 18 focuses the greatest bending moment atpre-engineered failure area 42 of the sacrificial link 40 between thefirst and second shaft portions 31, 32, deformation or breakage of theshaft 30 is limited to the sacrificial link 40, an easily replaceableelement.

Referring now to FIGS. 3 and 4, the structure and function of thepresent invention is illustrated in greater detail. The sacrificial link40 is generally cylindrical in shape, comprising a reduced diametercenter region 42 and spaced, opposing ends 41. The center region 42 issolid, while each end region 41 includes a socket 44 for receiving afree end of the upper or lower shaft portions 31,32 of the brush unit.Each socket 44 has an inner diameter approximating the outer diameter ofthe upper and lower shaft portion received therein. In the illustratedembodiment, upper and lower shaft portions 31 and 32 are the samediameter and sockets 44 are accordingly identical. This symmetrical,reversible arrangement is preferred since it reduces cost and simplifiesinstallation and replacement. It is possible, however, to use upper andlower shaft portions of different diameter or shape, and correspondinglydifferent sockets 44 at the ends of the sacrificial link 40.

The circumferential socket wall of each end 41 includes a pair ofopposed slots 45 extending from the end of each socket 44 downward alongthe long axis of the link 40. These slots effectively divide each socketwall into clamping halves to facilitate the secure attachment of thelink 40 to the upper and lower shaft portions 31, 32 of the brush unit.

Each socket 44 also includes bolt through-holes 46, extending throughthe wall of each clamping half. Through-holes 46 are aligned along anaxis perpendicular to the long axis of the link 40 and the plane ofslots 45. Upper and lower shaft portions 31,32 include matching boltthrough-holes 33 at their free ends. The sockets 44 in each end 41 ofthe link 40 are formed or milled to a depth permitting the alignment ofthrough-holes 46 and through-holes 33 when each end 41 of link 40 isconnected to the upper and lower shaft portions.

Link 40 in the illustrated embodiment is approximately twelve tofourteen inches in length and about two inches in diameter at its widestpoint (ends 41). It will be understood that other lengths and diameterscan be used to accommodate brush-unit shafts of varying lengths anddiameters.

While each of the socket ends 41 has an outside diameter ofapproximately two inches, the center region 42 is characterized by areduced diameter, in the illustrated embodiment approximately 1.25inches. The transition region from each socket end to the reduceddiameter center region of link 40 is defined by a solid tapered shoulderregion 43, in the illustrated embodiment approximately 1/2 inch inlength. Other taper lengths are possible, depending on the desireddeflection and strength characteristics of link 40 and its overalldimensions. However, the deflection characteristics of link 40 with theillustrative 1/2 inch taper have been determined to be preferred for thelink dimensions recited above.

Upper and lower shaft portions 31,32 are preferably manufactured fromsolid rods of steel, for example 7075 steel, while the sacrificial link40 in the illustrated embodiment is milled from a rod of commerciallyavailable steel known as "Stressproof". The following tables illustratethe deflection characteristics of this material in link 40 according tothe invention versus those in a one-piece prior art brush shaft:

    ______________________________________    STANDARD 7075 STEEL SHAFT (Prior Art)                                Permanent Set    Force Applied               Deflection Under Load                                Deflection    ______________________________________    400 psi    14"              0.5"    500 psi    19.5"            1"    550 psi    23"              1.5"    600 psi    25.5"            2.5"    ______________________________________

    ______________________________________    SHAFT WITH 11/4" DIAMETER STRESSPROOF    LINK WITH 1/2" TAPER                                Permanent Set    Force Applied               Deflection Under Load                                Deflection    ______________________________________    300 psi     7.5"            0.25"    400 psi    11"              0.5"    500 psi    14"              0.75"    600 psi    17.25"           2.75"    ______________________________________

The illustrative dimensions above result in a sacrificial link 40 whosebending strength is approximately 20%-30% less than that of shaftportions 31,32. This range has been found to provide an optimum balancebetween failure threshold and overall brush unit performance undernormal operating conditions and forces.

Of course, various grades of steel and even other metal alloys may beused to practice the present invention. In addition, shafts of varyingdiameters are also possible. The following tables illustrate thedeflection characteristics of some alternative diameters and materialstested for the sacrificial link described above, with the diameter givenfor the reduced center section 42:

    ______________________________________    11/2" DIA HRS                                Permanent Set    Force Applied               Deflection Under Load                                Deflection    ______________________________________    200 psi    3.75"            0.25"    300 psi    6"               0.75"    400 psi    9"               1.5"    Quit    ______________________________________

    ______________________________________    11/2 × 1/4 WALL THICKNESS HRS TUBING                                Permanent Set    Force Applied               Deflection Under Load                                Deflection    ______________________________________    200 psi     3.25"           0    300 psi     6"              0.25"    400 psi     8.5"            0.75"    500 psi    11.5"            1.5"    600 psi    18.5"            6.25"    Quit    ______________________________________

    ______________________________________    13/8" DIA STRESSPROOF                                Permanent Set    Force Applied               Deflection Under Load                                Deflection    ______________________________________    200 psi     3.25"           0    300 psi     5.75"           0    400 psi     8.25"           0    500 psi    10"              0.75" (0)*    600 psi    18"              3" (0)*    Quit    ______________________________________     *indicates clamping half failure

    ______________________________________    1" DIA STRESSPROOF                                Permanent Set    Force Applied               Deflection Under Load                                Deflection    ______________________________________    200 psi     7.75"           0.25"    300 psi    14.5"            2"    Quit    ______________________________________

    ______________________________________    2" DIA 6061-T6 ROD                                Permanent Set    Force Applied               Deflection Under Load                                Deflection    ______________________________________    200 psi     3.5"            0.75"    300 psi     6.25"           1"    400 psi     9.75"           2.5"    500 psi    13.25"           4"    Quit    ______________________________________

In operation, the sacrificial link 40 is detachably connected by socketends 41 to the upper and lower brush unit shaft portions 31,32. Asindicated above, the depth of each socket 44 in ends 41 is such thatthrough-holes 46 can be aligned with each of the correspondingthrough-holes 33 in the upper and lower shaft sections. To insure asecure engagement between the sacrificial link and each of the first andsecond shaft portions, a nut and bolt assembly 50 is fastened througheach bore defined by aligned through-holes 46 and 33. The slots 45 inthe circumferential walls of each socket end 41 permit the halves ofeach socket end to be clamped together upon tightening of the nuts andbolts 50, securely clamping link 40 to shaft portions 31,32 duringnormal brush operation. This clamping arrangement eliminates shearforces on bolt 50, resulting in a stronger connection.

The vehicle wash environment in which brush shaft 30 operates is often acorrosive one, and can cause the ends of shaft portions 31,32 to becomelocked in sockets 44 even after bolts 50 are removed. Socket ends 41 areaccordingly provided with tap holes 49 through which a bolt can bethreaded into contact with the stuck shaft. Advancing the bolt againstthe shaft in socket end 41 separates the stuck parts.

It will be understood that the foregoing is merely an illustrativeembodiment of the invention. Various other changes and alterations,apparent to those skilled in the art, can be made without departing fromthe scope of the following claims:

We claim:
 1. In a vehicle-cleaning brush unit having a brush-supportingshaft depending from a support unit, an improved shaft structurecomprising:a brush shaft comprising separate first and second shaftportions connected to a brush and a support unit, respectively, and aremovable sacrificial link connecting the first and second shaftportions to permanently deform under external bending load prior to thefirst and second shaft portions.
 2. Apparatus as defined in claim 1,wherein the sacrificial link comprises a sacrificial shaft sectionhaving two opposing ends connected to the first and second shaftportions, and a center region pre-engineered to fail before the firstand second shaft portions.
 3. Apparatus as defined in claim 2, whereinthe center region of the sacrificial shaft section includes a region ofreduced diameter.
 4. Apparatus as defined in claim 3, wherein the endsof the sacrificial link have a diameter greater than that of the centerregion, and further include regions of tapered diameter between theopposing ends and the center region.
 5. Apparatus as defined in claim 4,in which each opposing end includes a socket the inner diameter of whichis approximately equal to the diameter of each of the first and secondshaft portions.
 6. Apparatus as defined in claim 5, in which each of thesocket end regions is divided into clamping halves.
 7. Apparatus asdefined in claim 6, wherein the socket end regions include a clampingslot extending approximately the longitudinal length of the end region.8. Apparatus as defined in claim 7, wherein the sockets in the opposingends and the upper and lower shaft portions include through-holesaligned to define a throughbore when each of the first and second shaftsis connected to one of the sockets, further including a bolt extendingthrough the throughbore to clamp the socket clamping halves to the shaftsections.
 9. Apparatus as defined in claim 8, wherein each socket endregion of the sacrificial link includes a tap hole.
 10. In avehicle-cleaning brush unit having a brush-supporting shaft dependingfrom a motor drive unit, an improved shaft structure comprising:a firstshaft portion connected to the drive unit; a second shaft portionconnected to the brush; a sacrificial link removably connected to thefirst and second shaft portions, the sacrificial link designed topermanently deform in response to external force on the shaft prior toeither of the first or second shaft portions.
 11. Apparatus as definedin claim 10, wherein the sacrificial link comprises a sacrificial shaftsection having ends of a first diameter, sockets in the ends forremovable connection to the first and second shaft portions, and acenter region of a second diameter less than the first diameter. 12.Apparatus as defined in claim 11, wherein the first and second shaftportions are of a third diameter less than the first diameter andgreater than the second diameter.
 13. Apparatus as defined in claim 12,wherein the sacrificial shaft section further includes solid taperedregions between the ends and the center region.